The present invention relates generally to the field of welding systems, and more particularly to devices for creating high voltage, low current pulses used to generate and maintain arcs in such systems.
A wide range of welding techniques have been proposed and are presently in use. In general, welding of metals is performed by melting one or more base metals in a work piece, as well as an adder metal in certain applications. One particularly useful welding technique, particularly for precise or intricate welding, is tungsten inert gas (TIG) welding. In TIG systems, a metal electrode, typically made of tungsten, is provided in a torch, and is generally not consumed (i.e., added to the base metal) during welding. Electrical current is channeled through the electrode, and a flow of a shielding gas surrounds the electrode during the welding operation, generally provided by fluid conduits leading to the torch. An arc is struck between an electrode and the workpiece to melt the workpiece. Adder metal can be provided, but in general welding takes place by the fusion of the workpiece metals.
As opposed to certain other welding techniques, in TIG welding applications, it is desirable to strike and maintain an arc with little or no contact between the electrode and the workpiece, and the arc itself may be somewhat difficult to strike and maintain based upon the welding power alone. To aid in striking and maintaining the arc, then, the power supply may be designed to superimpose a high frequency, high voltage, low current waveform on a base waveform applied to the welding electrode via a welding torch. When welding with DC power, the high frequency pulse train may be provided only during start-up or loss of the arc. In AC welding, the pulse train may similarly be provided during start-up, but may also be provided continuously, where desired, so as to stabilize the arc and prevent the arc from being rectified or extinguished during polarity reversals of the AC waveform. The systems may sense whether an arc is established or maintained in order to provide closed loop control of the application of the high frequency waveform accordingly.
High frequency waveforms for establishing and maintaining arcs in TIG welding systems have typically been provided by a spark gap assembly that produces a high frequency waveform output when a relatively high voltage, low current input power level is applied to them. Conventional spark gap assemblies typically include “points” or flat surfaces between which arcs are established and extinguished at high frequencies. Conventional spark gap assemblies typically provide for some degree of adjustment of a gap between the points to sufficiently control the output frequency, and to reduce heating of the spark gap assemblies. Various more or less complex structures have been devised for mounting the points, for regulating the distance between the points, and for applying input power to the points and drawing output waveforms from them. Many such arrangements allow for a series of spark gaps to be provided, such as between opposing faces of multiple conductive elements that form the points.
While these assemblies generally function adequately, they are not without drawbacks. For example, traditional spark cap assemblies in welding systems are open to the atmosphere. Their performance and even their life can therefore be affected by the presence of humidity and airborne contaminants. Such contaminants may be quite common in the areas in which the welding systems are called upon to operate, and tend to accumulate on the spark gap assembly structures, particularly on the points themselves. Over time, the points are thus degraded, or even cease to function reliably to initiate and stabilize arcs. Similarly, it has been found that the points of traditional spark gap assemblies may be eroded or degraded over time due to the arcing that takes place in the normal production of the high frequency waveform. Such degradation, too, ultimately leads to the need to replace the entire spark gap assembly or the points, or to perform time-consuming manual adjustments of the gap between the points.
There is a need, therefore, for improved spark gap structures and techniques that avoid the drawbacks of the prior art.